O.k., here’s the problem: I have various .mpeg videos that I have downloaded using a peer-to-peer client. When I play a good fraction of these videos, and most of the larger ones (say over 5-7 MBs), they appear to be much shorter than they should be, and seem to jump from an intermediate point in the clip to the very end. If, however, I manually advance the clip nearly to the end of the progress bar, wait for it to “jump,” and then scroll back to the beginning of the progress bar, I will see the next portion of the clip. In essence, it seems as if sections of the video are layered on top of each other.
This is obviously a rather annoying problem, and I’m hoping someone has a solution–or at least some information on why this happens: is it an error in the download? A glitch in my video player? 
FYI, I’m using a Mac with OS 10.2.something and the Quicktime player. I’ve also tried playing some of the problematic clips in another freeware video player with the same results.
Help! Tech savvy Dopers to the rescue please!